Air conditioner defrost system

ABSTRACT

A novel system for detecting inefficiencies in a refrigeration circuit, such as an air conditioner system, is disclosed whereby a sensor sends a signal to a controller which will cause the compressor of the refrigeration circuit to be shut off when the evaporator is at risk of freezing out. The shutdown system of the present invention provides for controls that maintain the compressor in the shutdown condition allowing the evaporator a chance to recover, after which, the shutdown system will restore power to the compressor and will allow the operation of the refrigeration circuit to re-commence without experiencing a loss of efficiency that would occur if the refrigeration circuit continued to operate with a frozen evaporator for extended periods of time.

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The present invention relates to controls for air conditioner or refrigeration systems. More specifically, the present invention optimizes a refrigeration circuit for air conditioners or refrigeration systems when conditions cause the evaporator to freeze, thereby reducing the efficiency and impairing the operation of the circuit.

The history of refrigeration probably commenced in prehistoric times when it is known that food products, such as freshly killed game, where stored in caves or holes dug into the ground. From that humble beginning, techniques advanced to the use of ice, and then to a series of chemical admixtures, typically using water as a solvent and where the addition of a chemical such as potassium nitrate or saltpeter would generate an endothermic reaction that would lower the temperature of the solution. Subsequently, systems were introduced that employed vapor compression circuits, using agents like methyl chloride, sulfur dioxide, and ammonia. However, these chemicals all posed safety problems if they leaked or came into contact with people, so that when a new group of compounds called chlorofluorocarbons (CFCs) was discovered in the 1920s with properties that were ideally suited for vapor compression type cycling, the stage was set for the development of modern refrigeration systems. The ultimate CFC for this purpose was widely recognized as a group of halomethanes known collectively as “Freon” and modern systems optimized their compression and evaporation circuits for this particular chemistry.

By way of background, a compression-evaporation circuit commences with Freon in a liquid state. The Freon is then pumped into a radiator type device called an evaporator which, as the name implies, allows the liquid Freon to be gasified or evaporated within the radiator. The evaporator is located in the area where the cooling effect is desired. The phase change from liquid to gas causes the Freon chemistry to absorb a great deal of heat in the process. Freon's capacity for absorbing heat in this fashion is one reason why it did become such an effective refrigerant. In any event, the Freon gas is then directed into another radiator type device, but this time it is located in an area where the heat may be given up, and since when the Freon gas is allowed to discharge the heat it has absorbed, it again returns to the liquid stage, thus the second radiator type device is typically called a condenser. The liquid Freon is returned to a compressor (or pump) which sends it back through the system again, under pressure. This cycle is repeated over and over allowing massive quantities of heat to be absorbed and discharged and effectively and efficiently cooling the subject area in which the evaporator is located. Both the evaporator and the condensor are typically comprised of finned coils of tubing; usually copper tubing through which the refrigerant flows.

As may be appreciated, the development of the initial Freon based vapor compression systems did not stop in the 1920s. Since that time, both the Freon chemistry (termed a “refrigerant”) and the compressor-evaporator-condensor process (sometimes termed a “circuit”) have seen multiple improvements. Nonetheless, it has remained a long-standing problem that the refrigeration circuits of all types, whether these are used for refrigeration or for air conditions, experience some loss of refrigerant at times. When this happens, the efficiency of the circuits is lowered and one symptom of this is the condition where the evaporator freezes. In modern systems, the cooled and liquid refrigerant is sent to an expansion device first before entering the evaporator, allowing the evaporator to receive the refrigerant at a much lowered temperature, typically a twenty degrees temperature differential by design. When there has been a loss of refrigerant, or where there is insufficient heat loading on the evaporator (temperature differential of the subject area to be cooled is nominal or nonexistent), or there is reduced airflow over the evaporator, or where there is a restriction in the refrigerant circuit, it is possible for the temperature of the refrigerant to be lower than design parameters when it reaches the evaporator. When this happens, water that is typically collected on the evaporator coils can freeze (temperatures of refrigerant dropping below thirty-two degrees Fahrenheit). This so-called “freezing” of the evaporator, while it would perhaps initially seem to be consistent with the cooling of the subject area, works in the opposite manner. The freezing impairs the ability of air to flow over the evaporator coils and reduces the amount of heat that is taken up by the refrigerant. This effect continues until such time as the evaporator is allowed to warm up and the ice is melted.

This problem is the subject of a great many service calls for air conditioning and refrigeration systems, although the freezing of the evaporator may not be noticed until such time as it has impaired performance to a point that cooling is almost nonexistent. Many times the air conditioner or refrigeration system has been struggling with the underlying problem for weeks or months, before it reaches the point a service call is triggered. Meanwhile the unit is still consuming a great deal of electricity (or in some cases, natural gas) at great cost to the owner of the system. This results from the fact that the compressor and the fans continue to run even though the cooling performance is greatly reduced.

One aspect of this problem is that turning off the air conditioner or refrigeration equipment for a short period of time will restore much of the cooling capacity to the system. This restoration may be short-lived, but to the casual observer it appear that the cooling problem has been “solved” when in fact it will only be a matter of a short period of time before the freezing re-commences.

Surprisingly, the design of modern air conditioners and refrigeration systems do not account for this problem. In part this may come from the fact that the units perform flawlessly when first installed and the potential for guarding against the freezing of the evaporator does not appear as an observable problem. However, when tending to service calls on units and finding on a great many occasions that the freezing is the source for the call, it occurred to the applicant that there was a great deal of energy being wasted until the customer became motivated to call for help.

There are devices known in the prior art for controlling or responding to the freezing (sometimes referred to as “frosting”) found in refrigeration circuits. For instance, in U.S. Pat. No. 4,024,722 (McCarty) the controls for an air conditioning system sense the temperature of the system itself and keep the refrigerant above the freezing point while continuously operating. In U.S. Pat. No. 4,332,137 (Hayes, Jr.) a dual refrigeration circuit is controlled to selectively allow one circuit to be defrosted while the other circuit continues operation. Also in U.S. Pat. No. 5,586,448 (Ikeda, et al) teaches the use of a sensor and control means for an air conditioner in a vehicle to trigger an electrical defroster if the car is running (if the battery charging system is operating) and a means for controlling the heat exchanger of the unit to temporary heat the analogous component to defrost the system. Other systems are known where the refrigeration circuit accumulates icing over time and a defrost sequence is activated on a periodic basis to restore efficiency. These systems are typically used for cold storage where the refrigeration circuit is virtually operating on a continuous basis, unlike the present invention that is applicable to systems that may run for short durations during the day, or for a numbers of days at a time. Also the present invention is used in situations where periodic shutdown of the cooling can be tolerated notwithstanding the lack of a cold storage structure.

The foregoing examination of the problems that have been felt in the field of air conditioning and refrigeration applications illustrate the need for the present invention and the heretofore lack of a solution to the restoration of efficiency in such systems prior to resolution of any underlying system deficiency. Such attributes and benefits of the present invention are explored further.

SUMMARY OF THE INVENTION

A novel shutdown system for a refrigeration circuit comprises a sensor and a controller, where the sensor detects the condition when the evaporator in a refrigeration circuit is frozen and where the controller receives the information from the sensor and thereafter causes a remedial shutdown cycle to occur. Once the sensor detects the condition where the evaporator is no longer frozen, and the controller receives the information from the sensor and thereafter causes the refrigeration circuit to re-commence.

In an enhanced embodiment of the present invention, the controller for the shutdown system sends a signal to an alarm, the alarm comprising an audible alert or a visual alert, or a combination of both.

In another enhanced embodiment of the present invention, the controller for the shutdown system is capable of sending status reports to a master processor including but not limited to information regarding the existence (or lack thereof) of a frozen evaporator.

These and other attributes and benefits of a novel shutdown system for a refrigeration circuit will be discussed in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a refrigeration circuit with the shutdown system of the present invention installed.

FIG. 2 shows components of the shutdown system of the present invention with the shutdown controller and the shutdown sensor and related connections.

FIG. 3 shows a schematic representation of the shutdown system of FIG. 1 with an alarm/alert output device indicated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A novel shutdown system for a refrigeration circuit of the present invention is shown schematically in FIG. 1 as installed, in this instance, in an air conditioner system 10, which further contains an evaporator 12, evaporator coils 13, an evaporator fan 14, a condensor 16, condensor coils 17, a condensor fan 18, a compressor 20, a thermostat 22, air conditioner controller 24, a shutdown controller 30, a shutdown sensor 32.

The components of the shutdown system and refrigeration circuit are interconnected in ways that will be describe in more detail herein, however generally the evaporator 12, the condensor 16 and the compressor 20 are functionally connected by means of the refrigerant circuit 34. The shutdown controller 30 is connected to the shutdown sensor 32 by means of the shutdown input line 36, the thermostat 22 is connected to the air conditioner controller 24 is connected by means of the thermostat input line 46, the air conditioner controller 24 is also connected to the condensor fan 18 and the evaporator fan 14 by the condensor fan line 40 and the evaporator line 44, respectively, and also to the compressor 20 by means of the compressor line 42.

In FIG. 2, the shutdown system components 50 are shown as the shutdown controller 30, the shutdown sensor 32 and the shutdown input line 36, and also indicated is the set point dial 52, the air conditioner controller input line 54 and the compressor output line 56.

In use, the shutdown system will continuously be reading the condition of the evaporator through the shutdown sensor, which is typically a thermostatic device that is either pre-set at a particular temperature (in the vicinity of 32 degrees Fahrenheit) or which may provide a proportional output that can be read by the shutdown controller as a real time temperature. In any event, the signal from the shutdown sensor will not trigger any action unless and until a freezing condition of the evaporator is detected. This freezing condition may be considered a select temperature in the vicinity of 32 degrees Fahrenheit. At that point in time, the shutdown controller will transmit this condition to the air conditioner controller which will then cause the power to the compressor to shut off. It is understood that the power to the compressor is supplied by the compressor line, as is the power to be supplied to the evaporator fan is supplied by the evaporator fan line, and so forth. With the compressor off, the refrigerant will cease to course through the refrigerant circuit and no additional cooling will take place. This gives the evaporator a chance to “catch-up” and as its temperature elevates, the water that has frozen around the evaporator coils will melt and efficient functioning of the refrigeration circuit is restored. It is desired to keep the evaporator fan running during this time since it will expedite the melting of the frozen evaporator.

The timing for the length of the shutdown and the return to a “running condition” can vary. In one embodiment of the present invention, the shutdown controller may include a time-out relay that will restore the normal signal and therefore operation to the air conditioner controller. In another version of the present invention, the reading from the evaporator sensor will continue to be monitored until such time as a pre-set temperature is achieved. This may just be a temperature selected to reasonably reflect the melting of the frozen condition. Typically, principles of air conditioner operation would suggest that the evaporator temperature would run at a twenty degree Fahrenheit differential as compared to the condensor temperature. If the air conditioner controller is competent to detect this differential, that could become the trigger for restoration of power to the compressor and the resumption of operation. In any event, the objective is to provide a period of time for the evaporator to idle while conditions return substantially to normal, which may be considered a running condition.

The components of a shutdown system of the present invention as shown in FIG. 2 may readily be added to existing air conditioners or other refrigeration systems. There is a slight difference in the signal paths as shown in FIGS. 1 and 2, where in FIG. 2 the shutdown controller may be wired in series with the line power for the compressor. Basically, in an existing installation, the air conditioner input line originally meant to power the compressor, is patched into the shutdown controller and the compressor output line thereafter exits the shutdown controller and connects to the compressor. The shutdown controller is then set to interrupt the power supply coming from the air conditioner input line through the shutdown controller and then on to the compressor output line, when the freezing of the evaporator is detected. This method of installation does not require any compatibility with the internal circuitry of the air conditioner controls and it may be retroactively installed fairly easily.

The shutdown controller of FIG. 2 also provides an interface for controlling the temperature at which the shutdown occurs. This is accomplished by adjusting the set-point dial to a condition just above the point at which freezing of the evaporator would occur. This has the effect of allowing the shutdown controller to shut down the compressor directly at the set-point, or in the alternate, it could be the point at which a shutdown signal is transmitted to the air conditioner controller to pull in a shutdown relay. In either case, the result is the same in that the refrigeration circuit is beneficially interrupted.

It should be understood that electrical power to the shutdown sensor and the shutdown controller is necessary. While it is not shown specifically in the drawings, in practice, the shutdown controller may derive its power source parasitically from the air conditioner input line or it may be independently wired into a power supply that is common to the particular refrigeration application. As far as the shutdown sensor is concerned, it may derive its power source from the shutdown controller. Installation of the shutdown controller and shutdown sensor typically occurs within the housing for the particular refrigeration application. For instance, in the case of an air conditioner, it may be within the housing for the air conditioning unit itself. In other applications, or where it may be desired for any other reason, the shutdown controller and may be installed within a housing selected for such use, and with necessary ports for allowing the various lines to enter and exit as may be required. The shutdown sensor is typically located on or directly adjacent to the evaporator coils and will therefore be usually located within the housing for same.

Turning now to FIG. 3, a variation on the present invention is again shown in schematic form. In this case, the components of the refrigeration circuit remain essentially the same, and it is the addition of the alarm/alert module 60 which is connected to the shutdown controller 30 by means of the alarm/alert output line 62. In use, whenever a freeze-out condition is detected by the shutdown system, a signal is also supplied to the alarm/alert module through the alarm/alert output line. This allows an audible or visual indication of the existence of a freeze-out condition and may enhance an expedited response from the persons charged with the maintenance of the air conditioner or refrigeration systems. There is no reason for instance, that the alarm/alert module couldn't be located in a remote location where it can be monitored along with other controls in a building. In addition, a variation on this particular embodiment includes the fact that the alarm/alert signal may be directed as a signal meant for a computerized control system. In this case the signal may provide additional information such as confirmation that the shutdown system has been implemented, how long the compressor was shut down, and the ability for the computerized control to record and collect a database of such events so they can be analyzed to determine whether a close look is needed to determine whether or not repairs might be necessary. This last feature is particularly useful since the origin of a shutdown is many times related to a low charge of refrigerant which itself may be an indication of a leak or some other defect in the refrigeration circuit. Early detection and repair keeps the refrigeration circuit operating at high efficiencies which saves energy costs.

These and other attributes of the present invention can be employed by one skilled in the art to improve the performance of refrigeration circuits of many kinds. The teachings herein are meant to illustrate the way in which the invention may be practiced and do not and are not intended to limit in any way the scope f the invention. 

1. A shutdown system for a refrigeration circuit with at least an interconnected compressor, evaporator, and condenser, the shutdown system comprising: A shutdown sensor for detecting the condition of the evaporator; A shutdown controller for controlling the compressor; Where the shutdown sensor is calibrated to react to a freezing condition where the evaporator is at risk of freezing and where the shutdown sensor signals said freezing condition to the shutdown controller where the shutdown controller triggers the compressor to shut down for a select period of time and thereafter re-commences the operation of the compressor.
 2. The shutdown system of claim Number 1, where the select period of time the compressor is shut down by the shutdown controller, is the period of time until the running condition of the evaporator is restored.
 3. The shutdown system of claim Number 1, where the refrigeration circuit is an air conditioning application.
 4. The shutdown system of claim Number 1, where the refrigeration circuit is a cold storage application.
 5. The shutdown system of claim Number 3, where the shutdown controller triggers the operation of the compressor through an air conditioner controller.
 6. The shutdown system of claim Number 1, where the shutdown controller is connected in series in between the power supply for the compressor and the compressor and said shutdown controller is capable of interrupting the power to the compressor when the shutdown sensor detects a freezing condition.
 7. The shutdown system of claim Number 1, where the shutdown controller is connected to an alarm for audible or visual display of a shutdown condition.
 8. A shutdown system for a refrigeration circuit with at least an interconnected compressor, evaporator and condenser, the shutdown system comprising: A shutdown sensor for detecting the condition of the evaporator when its temperature is in a running condition, and when the temperature of the evaporator reaches a freezing condition; A shutdown controller that receives a signal relating to the conditions of the evaporator that are detected by said shutdown sensor, and where the shutdown controller is capable of interrupting the power supply to the compressor; Where said shutdown controller selectively interrupts the power supply to the compressor when it receives a signal from the shutdown sensor relating to the detection of a freezing condition, and where the shutdown controller restores power to the compressor when the shutdown sensor detects a running condition.
 9. A shutdown system of claim Number 8, where the shutdown controller sends a signal to activate an audible or visual alarm when a freezing condition is detected.
 10. A shutdown system of claim Number 8, where the shutdown controller communicates the condition of the evaporator as detected by the shutdown sensor, to a computer controller.
 11. A method for retrofitting a refrigeration circuit with a shutdown system to avoid the freezing of an evaporator, where the refrigeration circuit includes at least a compressor, a condensor and an evaporator, the steps of which comprise: Shutting off all power to the refrigeration circuit; Installing a shutdown sensor to an evaporator coil; Installing a shutdown controller in series with the power supply for the compressor and the compressor; Connecting the shutdown controller to the shutdown sensor; Restoring the power to the refrigeration circuit; Calibrating the set point of the shutdown controller to avoid the freezing condition of the evaporator; Confirming the set point for the shutdown controller operates to shutdown the power supply to the compressor when a freezing condition is detected; Confirming the restoration of power to the compressor when a running condition is detected.
 12. A method for retrofitting a refrigeration circuit with a shutdown system as in claim Number 11, where the method includes the additional step of: Monitoring the shutdown system of the refrigeration circuit by a computerized controller.
 13. A method for retrofitting a refrigeration circuit with a shutdown system as in claim Number 12, where the method includes the additional step of: Responding to the detection of a shutdown of the refrigeration circuit. 